As Woz put it today, Jobs was not a technical minded person. He hired others to do design, engineering, and development... he just wanted to make the choices as to what would sell. It was certainly something that he grew to be good at.
So I think in a major way that's who Apple needs to replace him: someone who does not know enough to think that something is too difficult to attempt. Someone is as baffled and wowed by technology as his customers. Someone who wants their devices to be stylish and easy to use.
Take someone like that, then give them near absolute power over styling and usability decisions. That's critical, because design by committee is almost always a death sentence for a product.